One known structure as a coupling structure between a main shaft and a generator rotor in the wind turbine generator is a structure where the generator rotor is coupled to a cylindrical sleeve and the sleeve is fastened to the main shaft. Such a structure is disclosed, for example, in International Publication Pamphlet WO2007/111425A1 (Patent Literature 1). Patent Literature 1 discloses a coupling structure where a rotor bearing (corresponding to a sleeve in the present application) to which a generator rotor is joined is fastened to a main shaft by shrink disk (corresponding to a shrink fit in the present application). In the coupling structure, the shrink disk is positioned between a generator and a bearing, where the rotor bearing is fastened to the main shaft. The shrink click includes a fixed disk and a movable disk and the fixed disk and the movable disk are coupled to each other by a bolt. The bolt is inserted in parallel with a central axis of the main shaft. When the bolt is fastened, the movable disk is pushed to the fixed disk so that an inner diameter of the shrink disk is reduced and the rotor bearing is fastened to the main shaft.
One problem in the structure where the sleeve is fastened to the main shaft is a difficulty in work operations for unfastening the sleeve from the main shaft and inserting the sleeve onto the main shaft. In order to secure fastening strength, it is preferable that the clearance between the sleeve and the main shaft is narrow. From such a viewpoint, the clearance between the sleeve and the main shaft is typically adjusted to about 0.1 mm. However, a narrow clearance between the sleeve and the main shaft makes it difficult to perform work operations for detaching the sleeve from the main shaft and inserting the sleeve onto the main shaft.
This problem is especially important when generator replacement is required after the wind turbine generator is installed. After the installation of the wind turbine generator is completed, it is very difficult to perform work operations such as detaching the sleeve from the main shaft over the tower and inserting the sleeve onto the main shaft. For example, in a wind turbine generator with an output of 5 MW class, the weight of the generator exceeds 100 tones. When wind turbine generator replacement is performed over the tower, the replacement must be performed while the generator is hoisted by a crane; however, it is significantly difficult to perform work operations for detaching the sleeve from the main shaft and inserting the sleeve onto the main shaft, while a heavy generator is being hoisted by a crane.